Is Leggatt replaceable?

If Leggatt and the captain had met on land, say in passing or at a common place for people to go, would their relationship be different? Would the captain still hold Leggatt with such high regards? Part of the reason why they are so close is that the captain sees Leggatt as a reflection of himself. This is definitely a factor in their relationship, but they would not have achieved such a powerful bond had they not been faced with such an unusual situation. The extremity of the situation in The Secret Sharer plays a huge role in the bond between the two men. Considering the captain's awkward position as the head of a ship which he knows very little about, he is not super confident. The crew doesn't trust him very much, and they shouldn't, since he is so young and inexperienced. He gives orders knowing that they may very well be wrong. When Leggatt comes onto the ship, the captain holds all the cards since he could easily expose Leggatt. Of course, he doesn't expose Leggatt, but takes his secret as his own and protects him in his room. The captain is able to escape his world of uncertainty about his job by taking in Leggatt. Their secret is so serious and so binding that it is only natural that their relationship would progress the way it did. They are both escaping something. So, does this make Leggatt replaceable? Could the captain have developed an equally powerful bond with another man, different from Leggatt, had he entered the ship under the same circumstances? The similarities between the two men that cause the captain to see Leggatt as his other are important to the story, but maybe the captain was desperate enough for someone to be close with that he could have connected with anyone.